Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

984
FXUS63 KLOT 260657
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
157 AM CDT Sun Apr 26 2026

.KEY MESSAGES...

- Severe thunderstorms Monday with all hazards possible, large
  hail, damaging winds and tornadoes. Heavy rain and localized
  flooding also possible.

- Potential for fog across primarily northeast Illinois through
  late this morning.

- Seasonable and dry conditions today, but cooler temps near
  Lake Michigan.

&&

.DISCUSSION...
Issued at 157 AM CDT Sun Apr 26 2026

Primary forecast concern remains severe thunderstorm and heavy
rain potential Monday into Monday evening.

Low clouds across southern lower MI and IN will continue moving
west early this morning with another mostly cloudy start
expected for much of the eastern cwa. There may also be fog that
develops as these lower clouds arrive. Confidence is low for
how widespread the fog may become and how low visibilities may
drop. Current fog trends appear on track for now, first
developing across northwest IN and then spreading west/northwest
across northeast IL. Assuming fog does form, the best potential
for dense fog appears to be over Lake Michigan and possibly
along the north shore toward UGN, which may persist through
midday. The low clouds are expected to lift and scatter through
late morning/early afternoon with increasing high clouds into
this evening.

The models are now trending faster with a leading round of
showers and thunderstorms Monday morning, possibly entering the
western cwa before daybreak Monday morning and possibly holding
together while moving across at least most of northern IL and
perhaps the entire cwa through midday. Some of this activity
could be marginally severe, as well as producing locally heavy
rain. While there remains some uncertainty with this time
period and how widespread the precipitation may become, it may
not have a large impact on the overall severe potential for
Monday afternoon into Monday evening with the overall setup
still quite favorable for severe thunderstorms. Initial
supercell development west/southwest of the area is expected to
eventually evolve into a squall line as it moves across the
local area. Where/when this happens is still uncertain and as
noted in the Day 2 outlook, the morning convection could allow
an outflow boundary to move back north as an effective warm
front. Where exactly that occurs is uncertain, but it would
serve as the focus for further tornado potential. Thus, despite
the increasing expectation for morning convection, the overall
severe trends remain largely unchanged, all hazards are
possible, though perhaps the largest hail potential may be
favored across the western half or so of the cwa.

Heavy rain remains a potential with a slight risk for the day 2
excessive rainfall now across the entire cwa. No change among
the models showing precipitable water values into the 1.5 inch
range. There remains the usual uncertainty from model qpf
forecasts, though there does seem to be a gradual increase from
swaths of 1-2 inches to perhaps swaths of 2+ inches, though
there also remains uncertainty for where these may materialize.
It remains a bit early for a flood watch, but if these trends
continue, a flood watch may be needed, especially if these qpf
amounts begin to more consistently appear over the Rock, Fox
and Des Plaines River basins.

Outside of any convection, prevailing south/southeasterly winds
on Monday may gust into the 35-40 mph range until late
afternoon, and then diminish some as they shift southwest Monday
evening.

There may be some lingering showers Monday night into Tuesday
morning across northern IL, but this potential seems to be
fading with the latest model runs. Another system lifting north
across the Ohio River Valley Tuesday afternoon into Tuesday
night could bring showers and possibly a few thunderstorms to
areas mainly south of the Illinois and Kankakee Rivers Tuesday
night.

A period of below normal temps is expected for the end of the
week with lows possibly in the mid/upper 30s for at least parts
of the area Thursday, Friday and Saturday mornings. Frost
potential will need to be monitored, which from this distance
appears Saturday morning would be the coolest with the best
chance for frost. cms

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1131 PM CDT Sat Apr 25 2026

The airspace remains under the influence of a large high
pressure system centered in southern Ontario, which is leading
to persistent easterly low-level flow. As a result, the
expectation is for a bank of IFR to MVFR cigs currently across
Ohio and far eastern Indiana to continue spreading westward
toward the terminals overnight. As the stratus bank moves over
Lake Michigan, cloud bases may build toward the ground leading
to either fog or LIFR cigs. Based on the current speed of the
stratus deck, continue to favor the early morning hours
(generally after 10Z) for cigs or fog to rapidly expand across
the terminals. So, will maintain the inherited TEMPO groups,
albeit with modest adjustments in time. Of course, will allow
trends to dictate AMDs through the night.

Whatever fog and stratus develops overnight should erode by
mid-morning. The remaining TAF period then looks quiet as
easterly winds gradually turn southeasterly and upper-level
clouds thicken.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago